Manhole covers and frames



March 17,.'1959k V, ELKlNGTQN 2,877,696

MANHOLE COVERS AND FRAMES Filed .June 9. 195s v 4 sheets-snaai '1 wllllllllllIl/ l INVENTOR V/ vm/v ELK/NGTON A TTORNEY March 147, 1959 v. ELKINGTON 2,877,696

IMNHQLE COVERS AND FRAMES VFiled June 9. 1955 v1 sheets-sheet 2 /NVENTOR V/ v/HN El. micro/v A T YORNE Y vMarch 17, 1959 v. ELKINGTON 'MANHOLE covERs AND FRAMES,

Filed June 9, 1953 4 Smets-sheet s lNvE/vroR AT7ORNE Y March 17, 1959 v, ELKlNGTON 2,877,696

' MANHOLE COVERS AND FRAMES Filed June 9, 1953 4 Sheets-Shea?. 4

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AHORA/5y United States Patent O i MANHOLE COVERS AND FRAMES Vivian Elkington, Dover, England, assignor to The Dover Engineering Works Limited, Dover, .England Application June 9, 1953, Serial No. 360,429

2 Claims. (Cl. 94-34) the casting. I have now discovered by experiment that-A considerable additional strength can be attained by giving the underside or base of the cover a downward or convex curvature with webs of lengths varying in'ac-y cordance with the curvatureextending upwardly fromthe upper concave side or face. Goodr results have already been obtained on loading tests with ka rectangular cover having the foregoing characteristic supported' as a' beam slung between two supporting ledges. The advantages `of the inventionare also attained-with a circular cover the underside of which is of convex or domed curvature and it is probable that the addition of webs extending from the underside of either rectangular or circular covers may still further enhance the strengthening effect, andstill further strength may be obtained by the use of corrugations in the base of the casting.

The invention consists broadlyv of a manhole cover having the underside of its baseco'nvexedly curved downwardly between flat surfaces adapted to seat on a flat ledge or ledges of the frame.

In order thattthe invention may be more readily'understood reference is hereby made to the accompanying drawings, wherein:

Figure 1 is an isometric cross vsection of a half 'of one form of frame and cover the other half being precisely similar.

Figure 2 is a plan view of a part of the supporting frame of Figure 1,

Figure 3 is a section of parts of a modified construction of the cover and frame shown in Figure 1,

Figure 4 is a section taken on line IV-IV of Figure 3,

Figure 5 is an isometric section showing a special construction of frame-bar,

Figure 6 is a plan of the corner of a frame built up from bars of the construction shown in Figure 5,

Figure 7 is a diametrical section of a circular cover according to the invention and Figure 8 is a plan of half this cover the other half being similar.

Referring to these drawings and particularly to Figures 1 and 2 the rectangular cover C is upwardly concave and further shaped to give a downwardly or convexedly curved bottom or base 2 the curvature running from iiat edge portions 3 which seat upon iiat surfaces or ledges 6 of the frame. Thus in eiect the cover is slung as a beam between supporting ledges on either side. Strengthening webs 4 extend upwardly from the curved base and run in both directions forming a number of upwardly opening rectangular cells which in practice are Patented Mar. 17, 1959 lled with concrete or other material. These crossing? webs extend upwardly to varying extents depending` 0n the curvaturev of the base so that they all terminate-in the same plane but not necessarily at the top surfaceofl thecover.

The base may be provided with downwardly project; ing ribs indicated at 2a to constitute runners for facilitat ing sliding movement of the cover as it is drawn olf from the frame and to give added strength to the structure. A- cover of the foregoing construction measuring 36 inches square clear opening weighing 7 cwts. of` which 3% cwts. is cast iron and balance is concrete filling supported in the manner described has been shown by tests tofbe capable of sustaining a load of tons applied to an area of l2 inches diameter located at its centre.`I It follows that in order to support such a load in nonrocking condition the framing 5 having at seating ledges 6- needs to be of adequate strength and in practice the frame is preferably constructed of bars having a corrugated supporting structure 9 proceeding downwardly from the flatseating ledges 6 (see Figures 5 and 6).

The enveloping walls 10 of these bars extend upwardly` great importance apart from the advantage of air andt Watertightness ensured thereby in that in order to ensure: non-rockingr characteristics it is necessary, not only Vthat the covers seat firmly on the ledges 6, but that they are restrained from any side or endways movement which" unless they iit closely, is liable to occur particularly' whenl heavily loaded vehicles pass over them. The

corners where the side and end elements of these bars join when connected up to constitute the rectangular frame are formed in the manner best shown in Figure` 6" the side bars being provided with flanges' 13 andvthe'end" bars with cooperating anged parts 14 so that'theelements' can be rigidly secured by bolts 15`andvfu'rther rigidity can be effected by bolts 16 shown in Figure 6.`

It`should b'e mentioned that these frame sections are -the subject of a separate application and form no part" of the present'invention except in" sofar as they for'n'y part of a combination which includes the special cover the subject of the persent invention.

In order to give adequate support to the side and end walls of the frame as a whole an outer casing 17 (see Figures 1 and 2) may be provided so as to provide for a concrete surround. This casing is preferably constructed of side and end elements which are coupled to the cover enveloping walls 10 of the frame by bolts 18 passing through spacer sleeves 19 and the channel thus formed between the outer casing and the frame is filled with concrete.

A modification of the cover hereinbefore described with relation to Figures l and 2 is shown in Figures 3 and 4. In this modification the downwardly convexedly curved bottom wall or base 2 of the casing is provided with corrugations 2b with the upstanding strengthening webs 4c proceeding upwardly from the centre line of some of the corrugations and short intermediate webs 4d extending inwardly from the end walls of the cover. In this modified construction the downwardly projecting ribs 2a not only resist rocking movement of the cover upon the convex bottom surface thereof, but also serve to bridge the -space between spaced apart corrugations, thereby facilitating the slidingmovement of the cover as it is drawn oi from the frame.

In Figures 7 and 8 a circular cover is `shown in accordance with the invention. In this case the downwardly convexedly curved bottom o1- base 2 of the cover is constitutedby a dome. vThe particular cover shown in Figures 7 and 8 is specially designed for housing lightingV equipment such as is used on aerodromes and aircraft land-L ingy surfaces arranged above a compartment which needs to belighted. The cover consists of a hollow upwardly' opening annulus adapted to be filled with concrete and vhas a central opening designed to accommodate a secondary cover (not shown) which carries the lighting equipment. As will be seen from the drawing the casting 20 had an annular ledge 21 to provide an annular seating for supporting the secondary cover carrying the lighting equipment, a ridge 22 being provided for cooperation with a groove in the wall of the secondary cover to ensure correct positional registration of the secondary cover with the main cover which latter is provided with radiating strengthening we-bs 20a. Thus on any failure of the lighting equipment the secondary cover carrying the lighting equipment can be removed and replaced. The construction of the cover as a whole renders them interchangeable and thus a fresh cover complete with its lighting equipment can be taken from store to replace the cover in use and the latter taken away for repair ready for replacement in any other frame the lighting equipment of whose cover has failed.

With these circular covers the requirement for the non-y rocking and air and Water tight characteristics, is of course, as important as with rectangular covers and for this reason accuracy of fit of the cover in its frame is important and this demands accuracy in the circularity of the frame. In order to ensure this the frame is cast in arcuate sections fitted together as indicated at 23 in Figure 8. In practice these sections are all interchangeable and a frame can be constructed fby taking the requisite number of sectionsusually three-and joining them upl to constitute a complete circular frame. By the means above described a circular cover and frame can be economically produced and being of circular form any necessary grinding to remove roughness and ensure firm seating and close fitting can be easily accomplished.

I claim:

1. A manhole assembly comprising, in combination, a rectangular manhole cover having a base with a downwardly facing tiat marginal portion and a convexly curved downwardly extending middle portion, upstanding strengthening webs extending upwardly from the down- Cil wardly curved base portion, said strengthening webs running in two directions to form cells adapted to be filled with a filler material and terminating in the same horizontal plane dening an upper surface; and a frame for supporting said cover, said frame havinga fiat seating ledge to seat thereupon said iiat marginal portions of the cover and a wall portion enveloping the peripheral rim of said cover and upstanding 'from the outer edge of said seating ledge, said cover abutting against the inner face of said upstanding wall, said upstanding enveloping wall portion terminating at its upper edge in a top rail, the wall portion between said rail and the flat seating edge of said frame f being corrugated, the peripheral surface of the rail facing the cover and the apices of the corrugations facing the cover -being flattened, the respective sides of the cover fitting said attened surfaces.

2. A manhole assembly comprising, in combination, a rectangular manhole cover having a base with a downwardly facing flat marginal portion and a convex middle portion having a concavely curved upper surface, upstanding strengthening webs projecting upwardly from said concave upper surface of the middle portion defining cells for receiving a ller material; and a frame supporting said cover, said frame having a flat seating ledge supporting said fiat marginal portions of the cover, a wall portion upstanding from the outer edge of said seating ledge and enveloping the peripheral rim of said cover, said wall portion terminating at its upper edge in a top rail and having corrugations between said rail and the fiat seating ledge of the frame, the peripheral surface of the rail facing the cover and the apices of the corrugations facing the cover being at, and the respective sides of the cover fitting said liat surfaces. 

